This project aims to characterize the formation and repair of DNA damage after treatment of mammalian cells with antitumor agents and to correlate the effects on DNA with cell killing. New techniques for the measurement of DNA damage in mammalian cells are being developed and utilized. The techniques are based on DNA alkaline elution, a filter procedure first developed in this laboratory. During the past year, further methodology improvement has permitted more reliable and reproducible measurements of DNA interstrand crosslinks, and a fluorometric DNA assay has been developed which permits DNA damage analysis without the use of radioactive labeling. Some human cell types having different sensitivities to chloroethylnitrosoureas, cis-Pt(II) or melphalan were found to have correlated extents of formation of interstrand crosslinks. Interstrand crosslinking by cis Pt(II) could be prevented or reversed by thiourea. Evidence was obtained that DNA inter- or intrastrand crosslinks are the major lethal lesion produced by cis-Pt(II). Aziridinylquinone (AZQ) and 4-mercaptocyclophosphamide derivatives produced DNA crosslinking effects typical of bifunctional alkylating agents. m-AMSA produced protein-associated DNA breaks typical for DNA intercalating agents.